As a method for analyzing individual particles optically by dispersing fine particles in a fluid and by causing the fluid to flow thinly, a flow cytometry has been developed. As an excitation light source for the flow cytometer, a laser light source having a wavelength band ranging from the ultraviolet to the infrared has been put into practical use, and a high power laser beam of 50 mW or more is used as laser output. Moreover, an optical coupling device having such a laser light source, or an optical fiber coupling device for propagating a laser beam having a wavelength band ranging from the ultraviolet to the infrared has been developed.
The optical coupling device has a structure in which a light emitting end face of the light-emitting element housed in a housing as a laser light source and one end of the optical fiber are arranged so as to face each other in the housing, and further the other end of the optical fiber is drawn out to the outside of the housing. As the light-emitting element, a laser diode (LD), a super luminescent diode, or a solid laser such as a YAG laser is used.
On the other hand, the optical fiber coupling device is configured so that optical fibers each fitted with a ferrule are attached from both sides to the interior of a cylindrical case so as to face each other, and configured to optically couple the optical fibers together (e.g., see Patent Literature 1).